The invention relates to fluid filters, more particularly to extended life filters, and more particularly to dual full-flow and bypass filters, and further particularly to cleanable and re-usable dual full-flow and bypass filters.
The invention relates to continuing development efforts relating to dual full-flow and bypass filters such as shown in Jiang et al U.S. Pat. No. 5,695,637, and to adaptation thereof for use in cleanable re-usable backflushable filter applications, such as shown in U.S. Pat. Nos. 5,462,679, 5,779,900, 5,858,224, all incorporated herein by reference.
Cleanable re-usable filters backflush the filter element with a cleansing fluid, such as air, in a direction opposite to the filtering direction. This has been found beneficial to extend the life of the filtering medium. This would also be desirable in a dual full-flow and bypass filter which includes a full-flow filter element providing a filtered primary flow therethrough, and a bypass filter element providing filtered secondary flow therethrough in parallel with the primary flow. The full-flow and bypass filter elements are annular and coaxially aligned, and the filtered fluid flows radially inwardly through each element into the hollow interiors thereof. A bypass tube extends axially in the hollow interiors of the filter elements and conducts filtered secondary flow axially therethrough after passage through the bypass filter element, and then merges the filtered secondary flow with the filtered primary flow in the hollow interior of the full-flow filter element. It is known to provide a venturi in the hollow interior of the full-flow filter element creating a low pressure zone aiding suction through the bypass tube of secondary flow from the more restrictive bypass filter element. This venturi-aided suction flow merges with the primary flow from the full-flow filter element and then flows to the filter outlet for return to a machine, such as an internal combustion engine.
In attempting to apply a backflush to the noted dual full-flow and bypass filter arrangement, it was found that little or no cleaning resulted. The present invention recognizes the cause of such problem, and provides a simple and effective solution. Namely, it has been found that the noted venturi suction effect, while desirable in the normal filtering operational mode, is undesirable in the cleaning cycle during backflush because it suctions the cleansing fluid to the filter outlet, effectively shunting same away from the full-flow and bypass filter elements which it is intended to cleanse. The present invention retains the venturi effect during the normal filtering operational mode, and shorts across and bypasses the venturi during the backflushing cleaning mode.